 Welcome, myself, Mr. Giridhar Jain, Assistant Professor in Electronics and Telecommunication Engineering Department, Valchan Institute of Technology, Sholapur. Now today we are going to discuss on temperature sensor PT100 and signal conditioning circuits. Now learning outcomes of this session are at the end of this session students will be able to describe temperature sensor PT100 and signal conditioning circuit. Second outcome is students will be able to design signal conditioning circuit. Now contents of the session are temperature sensor PT100 and its details, transducer bridge, instrumentation amplifier and design of instrumentation amplifier. Now first is temperature sensor PT100. Temperature sensor PT100 is basically RTD. RTD stands for resistance temperature detector, RTD. Now this PT100 is made up of platinum and it has a positive temperature coefficient of resistance. Means whenever there is an increase in temperature the resistance of PT100 increases at the rate of 0.385 ohms per degree centigrade. Resistance of PT100 at 0 degree centigrade is 100 ohm and its resistance at 100 degree centigrade is 138.5 ohm. Now using this temperature coefficient of resistance we can calculate the change in resistance due to change in temperature. Now change in resistance due to change in temperature is given by the formula change in resistance equal to temperature coefficient of resistance which is 0.385 ohms per degree centigrade multiplied by in the bracket final temperature minus reference temperature. Now characteristics of PT100 is linear over specified temperature range. Now we will see how to make use of this PT100 for sensing the temperature. For sensing the temperature using PT100 we require a transducer bridge as shown in the circuit. So this is PT100. So resistance of PT100 at 0 degree is RT and resistance of PT100 at a given temperature is RT plus minus delta R. Now this is a bridge resistances are RA, RB, RC and this is a PT100. Now applied voltage is VDC. Now this is point voltage at this point is VA and voltage at this point is VB. Now by potential divider voltage at point A is given by RA divided by sum of these two resistances RA plus RT plus minus delta R into VDC. Then voltage at point B is VB which is given by RB upon RB plus RC into VDC. Now VA minus VB is given by subtraction of these two voltages. So VA minus VB is equal to VDC in the bracket RA upon RA plus RT plus minus delta R minus RB upon RB plus RC. Now for design select RA is equal to RB equal to RC is equal to RT is equal to R. Therefore VA minus VB is given by VDC in the bracket R divided by in the bracket 2R plus minus delta R minus R upon 2R. So RR gets cancelled. So finally it becomes this term minus 1 by 2. That is equal to VDC plus minus delta R upon 2 in the bracket 2R plus minus delta R. Now voltage generated between point A and B which is VA minus VB is given by this equation and from this final equation VA minus VB is equal to VDC. This term is plus minus delta R divided by 2 in the bracket 2R plus minus delta R means VA minus VB is directly proportional to the change in resistance. And change in resistance is directly proportional to the change in temperature because characteristics of this PT100 is linear. This output differential output produced by this bridge which is VA minus VB is directly proportional to the temperature. Now we understand what are signal conditioning circuits. Now first pause this video and think on the following question. What is necessity of signal conditioning circuit? Now necessity of signal conditioning circuit is that output that is differential output of the bridge is very small of which need to be amplified for controllers. Therefore, to amplify the small amount of differential output produced by transducer bridge we require a signal conditioning circuit. Now in this design we are taking the instrumentation amplifier as a signal conditioning circuit. Now this is instrumentation amplifier. Now for this instrumentation amplifier 3 op-amps are used as shown in the circuit. This are R1, RF, R1, RF this is R4, R5 and this is again R4. This is VA and VB which is output taken from a previous circuit that is transducer bridge. Now voltage at point X is due to voltage VA and VB. So by using superposition theorem, voltage at point X when VA is acting alone and VB is grounded. When VB is grounded due to virtual ground this inverting terminal of lower op-amp goes to the ground and upper op-amp will act as a non-inverting amplifier. Therefore VX is equal to 1 plus R4 by R5 into VA and secondly if VB is acting alone and VA is grounded and VB is acting alone. So this VB due to property of op-amp voltage at inverting terminal will be VB. So upper amplifier will act as inverting amplifier. Therefore output is minus R4 upon R5 into VB. So this is VX. Similarly voltage at point Y is given by the equation VY is equal to. Now when VB is acting and VA is grounded again this will act as a non-inverting amplifier input is VB. So gain of non-inverting amplifier is again 1 plus R4 upon R5 into VB and when VA, VB is grounded and VA is acting alone then this will act as a inverting amplifier. Gain is minus R4 upon R5. So this is final equation for VY. Now if you look at the second operational amplifier. So second operational amplifier along with R1RF and this R1RF is nothing but a difference amplifier. Right? Therefore if you look at this equation VO is equal to RF upon R1 in the bracket VY minus VX. So this is the equation for output for the second differential difference amplifier. Now here we require VY minus VX. Already VX and VY is obtained. Now subtracting VX from VY we get VY minus VX is equal to this is VY, this is VX. Take the subtraction. Now this first two terms 1 plus R4 upon R5 is common. Therefore you will get VY minus VX equal to 1 plus R4 upon R5 in the bracket VB minus VA plus for the second term R4 upon R5 is taken common in the bracket VB minus VA. Now VY minus VX is given by VB minus VA is taken again common in the bracket 1 plus 2 R4 upon R5 and final output is given by VO equal to RF upon R1 in the bracket 1 plus 2 R4 upon R5 in the bracket VB minus VA. Now by looking at the final equation we can see that we can design the value of R1, RF, R4 and R5 for required gain of signal conditioning circuit that is instrumentation amplifier. Now this circuit can be used for designing a signal conditioning circuit as per requirement. RFI is made variable to adjust the gain. Now these are references Op-Ams and linear integrated circuits by Ramakan Gaiquat and second electronic system design by Vaibhav Tarathi, Electrotech Publications Sathara.